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12-21-2010, 03:47 PM   #1
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Aperture not working

Greetings,

I have acquired an 100mm f/4 Macro Takumar (SMC) that appears to have an issue with its aperture. It has an M42 mount with aperture lugs for metering without stopping down on my Spotmatic SPF. I cannot get it to stop down either manually or while on the camera when taking an exposure. Are there any tips on how to diagnose and fix this problem?

Thanks,

Tony

12-21-2010, 03:59 PM   #2
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There is a tiny pin on the lens mount. While depressing this pin (you may need something like the tip of a ballpoint pen), turn the A/M ring on the lens to M.
12-21-2010, 07:04 PM   #3
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I tried depressing both pins but neither seems to engage the aperture. Moreover, my 50mm f/2 SMC Takumar works fine on the camera, but the 100mm macro does not, even though they have the same mount.

Thanks
12-22-2010, 11:57 AM   #4
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I'm not sure about the Spotmatic F, so for simplicity, I'll skip it. With the lens off the camera, screw a rear cap on. That should press the tiny pin in. BTW, the tiny pin is a few degrees CCW of the square block on the mount, half-hidden here, not the larger chrome pin at the top:



Now slide the AUTO/MAN. switch so it says MAN. Set the aperture ring to f16 or so and the aperture blades should close. They should move whenever you change the aperture ring setting.

If you can't set the switch to MAN., it's that damned tiny pin. If you can get the switch to MAN. and still the blades don't move, the lens has to be disassembled for repair. The problem might be the blades or the aperture mechanism, both involving a lot of disassembly.

12-23-2010, 01:32 PM   #5
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Thanks for the info. Depressing the small pin and setting to manual does not resolve the problem, so it looks like a disassembly will be required.
12-23-2010, 08:14 PM - 1 Like   #6
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The blades might have oil on them (not typical for Takumars to get so oily they don't move) or a spot of rust sticking them together (seen this twice). Or the mechanism might be jammed, maybe it was dropped. The typical Takumar construction looks like my photo above, with no screws in the mount. There might be tiny screws in the DOF scale but they don't do anything except loosen the scale. So you have to start at the other end. I haven't seen this particular lens but it usually goes like this: unscrew the trim ring that says SMC Takumar 100/4 etc. It unscrews via the filter threads. Then you'll see 3 screws that hold on the filter thread barrel, take those off and the barrel comes off. Three more screws hold the focus ring on, remove those and the focus ring. Then those DOF scale screws finally become useful; remove them and the scale. Now slide off the aperture ring, being careful not to lose the bearing trapped between the ring and lens body, right where the orange diamond is. The aperture ring hides 3 screws that can be removed, and then you can take off the lens mount. To get to the aperture blades, you may have to remove front and rear lens groups. At that point construction varies but the screws aren't hidden any more so you can probably puzzle it out.
12-24-2010, 05:48 PM   #7
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Thanks Dave, for that information. I've come up with another bit of info about the lens. When it is set to manual, the larger pin only slowly raises back out if depressed. However, when in auto the pin pops right back after being depressed. Does this have any diagnostic value?

Thanks,

Tony
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